Switching mechanism



Nov. 14, 1944.

jH. c. HARRISON SWITCHING MECHANISM Filed Dec. 1o, 1945 5 Sheets-Sheet lNOV. 1,4, 1944. H. C, HARRlsQN '2,362,551

SWITCHING MECHANISM Filed DeC. l0, 1943 5 Sheets-Sheet 2 /NVEA/TOR H. C.HA R19/50N ATTO/NVE Y NOV. 14, 1944. H Q HARRISON 2,362,551

SWITCHING MECHANI SM Filed DeC. l0, 1943 5 Sheets-Sheet 3 W5/v To@ H. C.HARP/50N A T TORNE V Nov. 14, 1944. H. c. HARRlsoN SWITCHING MECHANISMFiled Deo. 1o, 1943 5 Sheets-Sheet 4 /Nl/E/vrof? H. C. HARRISON ATTORNEYNov. 14, 1944. H. c. HARRISON lSWITCHING MECHANISM Filed Dec. 10, 1943 5Sheets-Sheet 5 /NvE/v-ron H. C. HA R19/S 0N By ATTORNEY Patented Nov.14, 1944 SWITCHING MECHAN ISM Henry C. Harrison, Port Washington, N. Y.,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of New York Application December 10, 1943, Serial No.513,793

Claims.

This invention relates to switching mechanisms and particularly toimprovements in cross bar switching mechanisms employed in telephonesystems for establishing electrical connections.

An object `is to reduce the size and -weight of cross bar switchingstructures.

Another object is to improve, simplify and reduce the number of detailparts employed in such structures and to provide for greaterinterchangeability of such detail parts.

A further object is to construct the detail parts of the mechanism so asto make them self -aligning and self-adjusting with regard to air-gapsbetween electrical contact members in particular.

Heretofore cross bar switching mechanisms have been used in whichcoordinate contacting members were controlled for selection atintersecting points to establish electrical connections by means oflongitudinally movable horizontal and vertical intersecting control barsor tapes.

The present `invention relates \to cross bar switches of this generaltype in which vertically located contact-strips and horizontally locatedrows of contact springs are arranged for establishing of connections atintersecting points between groups of vertical strips and horizontalsprings.

A feature thereof is the provision of a series of horizontally locatednarrow insulation plates across the front of the switch structure and atthe front edges of which are embedded the vertical contact strips withcontact members projecting forwardly between the insulation plates. Eachhorizontal row of contact springs is embedded in a horizontally locatedsupporting plate of insulation material at the rear of the structure andis divided in groups one at each point where they are kcrossed by anequal number of vertical strips. Each group of springs is divided in twohorizontal layers with the springs appearing vertically opposite eachother in pairs, each pair constituting a single contacting means. A cardis provided at each cross-point inserted between the two layers ofcontact springs. These cards have oppositely located projections onwhich the contact springs are tensioned or sprung in such a manner thatthe cards will at the rear of the structure be held to pivot on a knifeedge on the associated rear supporting plate while the forward end ofeach card extends between two adjacent front insulation plates and restson or is tensioned by the springs against one side of one of theassociated vertical contact strips so thatV when the card is movedlaterally away from this contact strip, each pair of springs will makeyielding connection with its companion vertical strip. 'I'hus thesprings are aligned and selfadjusting to control the normal air-gapbetween themselves and the associated vertical strips.

Another feature is the arrangement andconstruction of the horizontal andvertical operating bars which are in the shape of thin flexible tapes.The vertical select tapes are slidably and partially embedded in thehorizontal front insulation plates and are moved longitudinally y orlifted by means of magnets arranged side by side at the upper ends ofthe tapes in an upper frame member of the switch structure. The`horizontal hold tapes are so arranged in relation to the vertical selecttapes and the forward projections on the card at each cross-point thatwhen a select tape is lifted, it will flex upwardly the hold tapes atthe point where these hold tapes cross the lifted select tape and sothat later when one of the hold tapes is shifted longitudinally by itshold magnet, the flexed portion thereof will engage the projection onthe card at the crosspoint of these two tapes, and move the card awayfrom the vertical strip against which it is normally resting ortensioned and thus cause the associated pairs of contact springs to makecontact respectively with the corresponding vertical strips at thiscross-point.

Another feature relates to the arrangement of the hold tapes and themagnets for operating these tapes. The thickness or verticalmeasurements of the horizontal front insulation plates may be equal orless than the vertical distance between them, which latter distance isdetermined by the required thickness of the operating card to give itstrength and rigidity and by the space required for the Contact springson opposite sides of the card. As this required width is exceedinglysmall, it is readily seen that the hold magnets must be placed quiteclose together. Hence the hold magnets must be arranged to meet theseconditions. To this end therefore the hold magnets for the whole switchstructure have been mounted in minor vertical groups on individualvertical brackets. These brackets in turn are arranged side by'side in astaggered relation at one side of the frame structure and connected attop and bottom to the bottom member of a U-shaped upright frame member.This bottom member for that purpose is partially cut out to accommodatethe brackets and thecoils of said hold magnets. This enables the holdtapes to be connected to the armatures of the hold magnets by variousextension pieces that are curved in one direction so as notto interferewith each other or with the magnet coils and armatures in the adjaventvertical groups. These brackets are combshaped and of magnetic materialso that each hold coil may be Wound on one of the comb members of thebracket serving as a core while the adjacent comb members serve asreturn polepieces for the associated armatures. One comb member isprovided between each two coils and serves as a return pole-piece forthese two adjacent coils and the armature for each coil is` looselymounted on the return pole-pieces on either side thereof.

The invention has been illustrated in the accompanying drawings inwhich:

Fig. 1 shows a front view ofy a cross bar switch structure in accordancewith the applicants invention;

Fig. 2 is a top View taken on line 2-2 of Fig. 1;

Fig. 3 is a cross-section taken on line 3--3 of Fig. 2.

Fig. 4 is an enlarged fragmentary front viewv of the switch mechanism ata cross-point;

Fig. 5 is an enlarged cross-section on line 5-5 of Fig. 2 taken throughone of the cards;

Fig. 6 is a fragmentary perspective of a card and other adjacent partsof the switch structure;

Fig. 7 is a fragmentary perspective of one of the hold coils and theassociated mechanisms and part of the bracket on which it is mounted;

Fig. 8 shows in part the arrangement of the brackets for the holdmagnets and the U-shaped left-hand supporting member of the frame; and

Fig. 9 is a partial perspective view of the mechanism at a cross-pointfor moving a card.

Referring now to the drawings in general, a number of cross barswitches, made in accordance with the applicants invention, may bemounted on top of each other and between a left-hand U-shaped framemember I and a righthand T-shaped frame member 2. Each switch consistsof a series of horizontally located supporting plates 5. of insulation,supported on the left-hand side on the U-shaped member I to which theyare clamped by means of bars such as 6 and clamped on the right-handside to the T-shaped member 2 by means of bars such as 8. The distancevertically between these plates is approximately equal to the thicknessof the plates. Between members I and 2 at the rear of the structure aremounted insulation mounting plates such as ID. In each of these areembedded or clamped a series of rows of horizontal contact springs ingroups of six. The first one of these groups is shown at Fig. 2 markedwith the numeral I I. Associated with these horizontal groups of contactsprings are six vertical contact strips such as group I2 for group IIand others in the same corresponding positions in the verticaldirection. The switch illustrated may have a capacity of ten groups ofsix contact springs each in each horizontal row and having twenty suchhorizontal rows, so that, each vertical row of six contact strips suchas I2 may be associated with twenty groups of contact springs in twentydifferent horizontal rows, thus making it possible to establish twohundred connections in a switch of this type. The vertical stripsy areembedded in the front insulation plates and are provided with forwardlyextending portions such as I5, each having a contact I6 in a verticaldirection secured on the right-hand side thereof. These extensions I5are located between the horizontal insulation plates 5 and are as widein a vertical direction as the distance between the plates with thecontacts I6 of the same width. Each group of six contact springs besidesbeing anchored or embedded in a plate I is also mounted on an individualoperating card such as 20. One of these cards is shown in cross-sectionin Fig. and is provided with a central longitudinal rib 2| and flatopposite sides 22 and 23 which are narrower than the rib 2|. From thesedat sides protrude on opposite sides and approximately the middlethereof, circular knobs, such as 26, one for each spring, and similarknobs, such as 2'I, located towards the front of the card. The rib 2|ends at the rear in a V- shaped portion as shown at 30 engaging a knifeedge portion 3I on the associated rear plate I0, and this rib 2I extendsforwardly beyond the sides 22 and 23 and past the vertical strips I2into a portion 33 of substantially square crosssection. Springs II areso tensioned and arrangedr on these knobs 2B and 21 on a card that theywill hold the portion 30 against the knife 3| to be rotated thereon andthe front portion 33 pressed against the nearest right-hand verticalstrip as shown, for example, in Fig. 2 where the portion 33 engages thestrip 34 and so that the forward contacting ends of the contact springswill be positioned a certain definite distance away from theirassociated contact strips. The required air-gap between the springs andthe strips is thereby provided without any undue or elaboratearrangements for adjusting these air-gaps. In fact, these air-gaps aredetermined practically automatically by having the forward portion33engage the strip 34 and thus locating all the springs in the properdistance from their associated contact springs. To establish theconnections between the springs and the associated contact strips, theforward ends of the cards 20 need therefore merely be moved towards theleft for a short distance. The cards and the springs mounted thereonoccupy extremely small spaces. They are merely wide enough to providethe necessary strength and as the springs are located in pairs onopposite sides of the flat sides 22 and 23, the actual distance occupiedvertically by each card is comparatively small. This determines thevertical distance between the horizontal front plates 5 and allowssufficient room for the rear plates I0 to be mounted one on top of theother as shown for example in Fig. 3. The vertical space occupied by thetwenty horizontal rows of contacts is therefore small, compared withordinary standard cross bar switches of this capacity. In fact, thevertical over-all dimension may be reduced to two-thirds or more thanthe corresponding dimension in prior switches. On the other hand-thehorizontal width of the card 20 is only that required for a central riband the fiat sides toi provide strength and a sufficient distancebetween the pairs of contact springs to mount the associated contactstrips and provide the necessary air-gaps, thus the horizontal width ofthe switch may also be reduced perhaps to one-third less than thestandard switches. The groups of six pairs of springs at eachcross-point will as is evident make six separate connections, each pairof springs making one electrical connection with the associated contactmember I6.

The arrangement for operating these cards to establish connections atcross-points between contact springs and associated contact strips willnow be described. The vertical select bars which are in the form oftapes such as 50 are each located centrally between two adjacentvertical rows of contact strips and are partially embedded for slidablemovement in slots across thefront insulation plates as shown clearily inFig. 6, for example. Each of these bars is connected to an armature suchas 52 controlled by an associated magnet 53. There are ten of thesemagnets mounted on a common horizontally located combshaped member 54 atthe top of the switch, every other comb-tooth of which is surrounded bythe winding of a separate magnet. The intermediate comb-teeth serve asreturn pole-pieces for adjacent windings. The armatures 52 are looselysuspended between adjacent'l pole-pieces by means of brackets such as 55and 56 secured to said pole pieces. Each bracket serves as a suspensionmeans for the adjacent armatures and is for that purpose bifurcated orslit through the center. Each armature is provided with a downwardlyextending insulation card such as 51 which controls a series ofoff-normal springs 58. It should be noted that each vertical select baris provided with forwardly extending projections such as 60, one foreach horizontal hold bar, the purpose of which will be describedhereinafter.

In the present switch there is provided as stated twenty horizontalrowsof contact strips and a hold bar is provided for each row such asfor example 62 for the first row. These hold bars, which are in the formof flexible tapes, must of necessity be mounted close together to fit inbetween the rows of springs and are slidably mounted on the U-shapedbracket and the T-shaped bracket 2 in slots in the associated members 6and 8. It is further seen that there will not be room to mount the holdma/gnets for these bars one above the other as is the usual practice.They are therefore mounted in groups of five in staggered relation asshown for example in Fig. l on individual vertical mounting bracketssuch as bracket 63 for the first group of' five magnets and three otherbrackets for the remaining three groups of five magnets each. Thesemounting brackets 63 are mounted by means of angle pieces such as 64 and65 on the forward bottom member of the U--shaped frame member l whichfor that purpose is cut out to form openings as indicated for example inFig. 8 at 66. The upper pieces 64 are mounted on one connecting portion61 of the forward bottom member and the lower pieces 65 are mounted on alower connecting portion 68 as shown in this Fig. 8. These brackets aremounted side by side and being four in number will accommodate thetwenty hold magnets. It should be noted that they are mounted in astaggered relation on the connecting portions 61 and 68 to shift themagnets on the succeeding brackets a short distance downwardly lookingat Fig. l so that theY first magnet on the first bracket will controlthe first hold bar, the first magnet on the second bracket the secondhold bar, the first magnet onthe third bracket the third hold bar andthe first magnet on the fourth bracket-the fourth hold bar and so on sothat the succeeding magnets on succeeding brackets will controlsucceeding hold bars of the group of twenty. Each hold bar is connectedto an armature such as 69 for the first magnet'l 10 on the first bracketby means of an intermediate connecting link 1| which connects at 12 tothe first bar 62. It should be noted, of course, that the brackets 63are of the same design as the bracket 54 for the select magnets, thatis, these brackets are provided with comb-members on every other one ofwhich is. mounted the winding of the associated select magnet. Theintermediate comb-members serve as return polepieces for the adjacentmagnets and 'themember on which windings are located serve as the cores.The armature 69 straddles the three adjacent members and is mountedloosely by means of. brackets such asy 15 and 16 connected to theadjacent pole-pieces on opposite sides of the armature. These bracketsserve also the purpose of mounting adjacent armatures such as bracket 16serving as amounting means for the armature 69 for the first magnet 10Aand for the armature 18 for the second magnetw 19. In order that theconnecting links between the armatures of the hold magnets and the holdbars shall not interfere with each other, they are of course ofdifferent corresponding lengths to reach from the hold bars to thearmatures for the succeeding brackets and also bent or formed in aU-shaped formation towards the front to avoid the intermediate magnets.For example, the connecting link for the rst magnet 8| on the lastbracket 82 will have to be vbent or formed in a U-shaped formation toavoid the magnet and armatures of the intermediate hold magnets such as83, 84 and 10, while, for example, the connecting link 86 for thearmatures of the rst magnet 83 on the second bracket is bent to anotherci-shaped formation to avoid magnets 84 and 10 and their associatedparts. This formation of a connecting link is clearly illustrated inFig. 7. On the rear portions such as, for example, 81 yof the bracket 63is mounted fo-r each hold magnet an insulation block E9 in vwhich isembedded a series ofoffnormal springs such as 90. These springs extendrearwardly towards the rear of the structure for terminal connectionsand forwardly to cooperate with stationary contacts 82 connected to thefront spool head 93 of magnet 10 when the armature 69 is attracted andreleased under control of an insulation plate 94 attached to thearmature 69. This arrangement is similar to the o-normal springr`arrangement for the select bars.

A description will now be made of the function of they select bars andhold bars at each cross-point to cause `a card 20 to be moved when thecorresponding select bar .and hold bar are actuated. The mechanism forthis purpose is as follows. .If special attention is given to Figs. 6and 9 it will benoted that the card 20 at its forward end 33 is providedwith a U-shaped metaly clip 96, securely fastened thereto by having theupper side of clip 96 bent downwardly into a V- shaped depression 91 andthe lower side of slip 3B bent upwardly into a cut-out 98 as shown at99. This clip 96 is also provided with a lip 00 that extends forwardlytowards the right looking at Fig. 9. located the associated hold tape 62and on the left-hand side of it is located the associated select tape50. If the select tape I50 is lifted by its associated magnet, it willbe observed that the projection 60 thereon will-engage an enlargedportion |02 on the hold tape 62, and thereby due to the flexibility ofthe hold tape 62 causesl this tape to bend upwardly and also with aslight twist in the upward direction. This upward bending of the holdtape B2 is limited to the particular intersecting area at which thisselect tape is actuated due to projections such as |03 on the oppositeside of this intersecting area. The remainder of the hold tape 62 willbe unaffected at any other intersecting area by this bending action.This bending and twisting of the hold tape now causes a further forwardextension |04 to be raised to a position above the lip |00 on the clip96, as shown in dotted lines in Fig. 9.

Just below the end of the tip 33 is' When the hold tape 62 is then movedtoward the lett by its associated hold magnet, this projection |04 willtherefore engage the tip 33 in the cutout portion 98 at point |00, andthereby cause the card to be rotated on its pivotal point at 30. Themovement of the card in this manner will shift the contact springstoward the left looking at gures such as 2 and 6 and permit thesecontact springs to contact With the associated contact strips I2. Thismovement of the card 20 toward the leit need not be particularlyaccurate as long as it is suiiicient to make the springs Contact withthe strips as the springs are movable away from the hubs 2l so that theywill, if the movement of the hold tape 62 is excessive vneverthelessyielding contact with the strips. The select tape may now be returnedtoV normal while the hold tape with its projection |04 will be heldabove the lip |00 on the clip 96 at this particular intersecting pointand the connection will be maintained by this hold' tape in actuatedposition as long as desired. When the hold magnet releases, the tape 62will return to normal and release the card 20 for return to normal, andthe projection |04 slip off the lip s |00 and assume its normal straightposition.

From this description of the applicants invention as embodied in a crossbar switch, it is readily seen that a good many of the detailed partsare interchangeable such as the magnetic structures in the supportingbrackets and easily removed individually for repair if necessary. Therequired distances between the coordinated con tact strips and contactsprings are exceedingly small and thus the associated parts of themechanism are adapted for these smaller dimensions so that the overeallsize of the switch mechanism is considerably reduced. The sizevertically and horizontally may therefore be reduced to approximatelyone-third less than standard switches of this general type. As all thedetail parts of this mechanism are extremely small and light, flex-`ible and narrow in construction, the weight of this switch may also beconsiderably reduced to approximately one-quarter of the weight ofstandard switches of this general type known in the art. Parts of thismechanism are also easily manufactured as it will be noted that the card20, for example, may be molded in one piece with the clip 96 easilyattached to the end 33. 'I'he insulation plates are simple, easilymolded and standardized While the contact strips, select bars and holdbars may be punched out of very light ilexible material in simple forms.The contact springs may also be easily assembled in horizontal holdingstrips such as I0 and clamped together by eyelets such as ||0 shown inFigs. 3 and 6 in particular.

What is claimed is:

l. In a cross bar switch, coordlnately arranged cross bars in which thehold bars are flexible and located horizontally while the select barsare l0- cated vertically, horizontally located insulation plates,vertical contact strips secured to the plates, horizontally located setsof contact springs at each cross-point of the coordinate bars, anoperating card secured to each set of contact springs and controlled bysaid springs so as to normally engage one of the associated verticalstrips under tension of said springs to regulate the normal air-gapbetweenthe springs and thecorresponding contact strips and further soarranged that when the card is moved away from said vertical strip, saidsprings will yieldingly make contact with the respective verticalcontact strips, a mag- INI its

net for each select bar for shifting it longitudinally, a magnet foreach hold bar for shifting it longitudinally, means on said select barsand hold bar for flexing all hold bars by any select bar when shifted atthe cross-points where the shifted select bar crosses the hold bars,means on any hold bar operative after it has been flexed and when it isshifted for engaging the card at the point where this hold bar crossesthe shifted select bar and for moving it to shift the associated springsinto engagement with the associated vertical strips.

2. In a cross bar switch, coordinately arranged cross bars in which theselect bars run in a. vertical direction and the hold bars in ahorizontal direction and in which the hold bars are in the form offiexible tapes, vertically running contact strips arranged in sets, onefor each vertical row of cross-points of said bars, horizontally runningContact springs arranged in sets, one set for each cross-point, each setextending in the horizontai plane at right-angles to the associated setof vertical strips, a stationary support for one end of said springswhile the opposite ends of said springs are free to move in contact withcorresponding vertical strips at corresDOnding crosspoints, a card foreach set of springs so controlled and arranged as to be held by saidsprings in a position where the card rests at one end against saidstationary support as a pivotal point, while the other end of the cardis held against an associated vertical contact strip so that when thecard is moved away from said contact strip, the free ends of saidsprings will yieldingly contact with the associated strips and meansassociated with said select bars and hold bars and said cards wherebywhen a select bar is moved it lifts the hold bars ina position so thatwhen any one of said hold bars is subsequently moved it will engage thecard at the cross-point of said moved select bar and hold bar and moveit to cause the springs thereon to connect with the associated strips.

3. In a cross bar switch, e, frame, a group of horizontally mountedinsulation plates in said frame, vertically mounted contact strips onsaid plates, another group of horizontally mounted insulation plates insaid frame, a, horizontal row o! sets of springs mounted in each of saidlastmentioned plates, each row extending between two of saidfirst-mentioned plates with each set adjacent a particular correspondingset of contact strips, an operating card mounted on each set of springs,each card having a projection tensioned by the springs to engage one ofthe associated contact strips to x the air-gap between the associatedsprings and the corresponding contact strips, said card being so mountedon said springs that when the card is moved away from said contact stripeach spring thereon will make flexible contact with a correspondingassociated contact strip, a horizontally mounted magnetic core on saidframe, select magnet coils and associated armatures mounted on saidcore, a vertically located select tape attached to each armature andassociated with a corresponding vertical row of cards, a series ofvertically mounted cores on said frame, a group of hold magnet coils andassociated armatures mounted on each core in said series, a horizontallylocated flexible hold tape attached to' each of said last-mentionedarmatures, one of said hold tapes associated with each horizontal row ofcards, means integral with said select tapes and hold tapes andcooperating at each cross-point with an associated card to move it tocause its attached springs to engage the associated strips in responseto the shifting of the corresponding `select tape and hold tape by theattached armatures when attracted by the assoelated coils and cores.

1l. In a cross bar switch, a group oi' horizontally located insulationplates one on top oi' the other and spaced apart a distanceapproximately equal to their thicknesses, two vertical frame members,means for mounting said plates between said frame members towards theiront of the switch, Contact strips vertically mounted across saidplates partially embedded therein and having forwardly extendingcontacting projections between each two adjacent plates, another groupoi' horizontally located insulation plates one on tcp ci the other,means for mounting said last-mentioned plates at the rear of the switchbetween said vertical frame members with each or" said rear platesoccupying position vertically corresponding to the space between twoadjacent iront plates, rows of springs embedded in said rear plates andextending with their i'ree ends through the openings between adjacenti'ront plates in sets, each set comprising van upper and a lower layerof springs and eX- tending past vertical contact strips in pairs, eachpair comprising a spring from the associated upper and lower layers of aand each parA arranged for movement into contact with the correspondingextension on a vertical strip, an operating card between the two layersof each set of springs, having a knife edge at one end resting in adepression in the associated rear plate and having its opposite endresting against one of the associated vertical strips and having meansengaging the associated springs to tension said springs so as to presssaid card against said vertical strip and when said card is moved withits knife edge remaining as a pivot away from said vertical strip, saidset of springs may yieldingly maire contact with the associatedrespective vertical strips, a horizontally located magnetic Vcoresecured between said frame members above the upper insulation plates, aplurality of select magnets and associated armatures mounted on saidcore, a vertically located select tape attached `to each armature, oneselect magnet, armature and select tape being provided for each verticalrow of cards, a plurality of Vertical magnetic core brackets arranged inparallel relation and attached to one of said frame members, a pluralityof hold magnets on each bracket, an armature for each magnet, ahorizontally located flexible hold tape attached to each armature formovement thereby in a longitudinal direction, one hold magnet, armatureand hold tape being provided for each horizontal row of cards, eachselect tape and each hold tape being provided at each cross-point with aprojection each select tape adapted to lift the hold tapes at thecross-points of said tapes when the associated select m'agnet isactuated and the projection on a hold tape at the cross-point of saidhold tape and an actuated select tape operative when this hold tape isactuated by its hold magnetto engage the associated card and move thiscard to cause its associated set of springs to connect with theassociated vertical Contact strips at said cross-point.

5. In a cross bar switch, coordinately arranged cross bars in which thehold bars are flexible and located horizontally While the select barsare located vertically, horizontally located insulation plates, verticalcontact strips embedded in said plates, horizontally located sets ofcontact wires at each cross-point of the coordinate bars, an operatingcard of insulation material secured to each set oi contact Wires andcontrolled by said Wires so as to normally engage one of the associatedVertical strips under tension of said wires to regulate the normalair-gap between the wires and the corresponding contact strips andiurther so arranged that When the card is moved away from said verticalstrip, said wires Will yieldingly make contact with the respectivevertical contact strips, a magnet for each select bar for moving itlongitudinally, a magnet for each hold bar for moving it longitudinally,a projection on each said select bar and a projection on each said holdbar at each cross-point of said bars, said projections on a select barwhen moved being in 'position to engage the corresponding projections onall the hold bars Where these bars cross and flex said hold bars at saidcross-points, an additional projection on each hold bar at each pointWhere it crosses the select bars,` said last-mentioned projections on ahold bar operative after said hold bar has been flexed HENRY c.HARRISON.

